In which one of the following situations will the numerical value of distance travelled be equal to the magnitude of displacement?
(a) A cyclist rides 6km east, then 2km west and stops
(b) A runner completes one full lap on a 400m circular track and stops where he started
(c) A bus travels 5km north in a straight line without turning back and halts
(d) A hiker walks 3km up a hill and later returns halfway down